The presently disclosed embodiments are directed to imaging members used in electrostatography. More particularly, the embodiments are pertaining to electrophotographic imaging member which has improved imaging layer(s) formulated to consist of a novel polycarbonate binder that has chemical vapor contaminant resistive property to preserve copy printout quality. The present disclosure relates to all types of electrophotographic imaging members used in electrophotography.
In electrostatographic reproducing apparatuses, including digital, image on image, and contact electrostatic printing apparatuses, a light image of an original to be copied is typically recorded in the form of an electrostatic latent image upon a photosensitive member and the latent image is subsequently rendered visible by the application of electroscopic thermoplastic resin particles and pigment particles, or toner. Flexible electrostatographic imaging members are well known in the art. Typical electrostatographic imaging members include, for example: (1) electrophotographic imaging members (photoreceptors) commonly utilized in electrophotographic (xerographic) processing systems; (2) electroreceptors such as ionographic imaging members for electrographic imaging systems; and (3) intermediate toner image transfer members such as an intermediate toner image transferring belt which is used to remove the toner images from a photoreceptor surface and then transfer the very images onto a receiving paper. All the electrostatographic imaging members are prepared in either flexible belt form or rigid drum configuration. For typical flexible electrophotographic imaging member belt, it comprises a charge transport layer, a charge generating layer, and optional layers on one side of a supporting substrate layer and does also include an anti back coating on the opposite side of the substrate to imaging member flatness. For a typical flexible electrographic imaging member belt, it does, however, have a more simple material structure; it includes a dielectric imaging layer on one side of a supporting substrate and an anti-curl back coating on the opposite side of the substrate to render flatness. Alternatively, the electrostatographic imaging members can also be a rigid member, such as those utilizing a rigid substrate support drum. For these drum imaging members, having a thick rigid cylindrical supporting substrate bearing the imaging layer(s), there is no exhibition of the curl-up problem, and thus, there is no need for an anticurl back coating layer.
The flexible electrostatographic imaging members may be seamless or seamed belts. Seamed belts are usually formed by cutting a rectangular sheet from a web, overlapping opposite ends, and welding the overlapped ends together to form a welded seam.
Although the scope of the present embodiments covers the preparation of all types of electrostatographic imaging members in flexible belt design or rigid drum configuration, however, for reason of simplicity, the discussion hereinafter will focus and be represented only on flexible electrophotographic imaging member belts.
One type of flexible composite photoconductive layer used in xerography is illustrated in U.S. Pat. No. 4,265,990 which describes a photosensitive imaging member having at least two electrically operative layers. One layer comprises a photoconductive layer which is capable of photogenerating holes and injecting the photogenerated holes into a contiguous charge transport layer. Generally, the two electrically operative layers are supported on a conductive layer support substrate, with the photoconductive layer being sandwiched between a contiguous charge transport layer and the supporting conductive layer. In this negatively charged imaging member, the charge transport layer is therefore the top outermost exposed layer. In the alternative imaging member design, the charge transport layer is, however, sandwiched between the supporting electrode and a photoconductive layer. Since the typical flexible electrophotographic imaging members exhibit undesirable upward imaging member curling-up after completion of the electrically operative layers, the application of an anticurl back coating onto the backside of the support substrate is necessary to provide the appropriate imaging members with desirable flatness.
The flexible photosensitive members having at least two electrically operative layers, as disclosed above, provide excellent electrostatic latent images when charged in the dark with a uniform negative electrostatic charge, exposed to a light image and thereafter developed with finely divided electroscopic marking particles. The resulting toner image is usually transferred to a suitable receiving member such as paper or to an intermediate transfer member which thereafter transfers the image to a receiving member such as paper.
In the case where the charge generating layer is sandwiched between the top outermost exposed charge transport layer and the electrically conducting layer, the outer surface of the charge transport layer is charged negatively and the conductive layer is charged positively. The charge generating layer then should be capable of generating electron hole pair when exposed image wise and inject only the holes through the charge transport layer. In the alternate case when the charge transport layer is sandwiched between the charge generating layer and the conductive layer, the outer surface of the charge generating layer is charged positively while conductive layer is charged negatively and the holes are injected through from the charge generating layer to the charge transport layer. The charge transport layer should be able to transport the holes with as little trapping of charge as possible. In flexible imaging member belt such as photoreceptor, the charge conductive layer may be a thin coating of metal on a flexible substrate support layer.
As more advanced, higher speed electrophotographic copiers, duplicators and printers were developed, however, degradation of image quality was encountered during extended cycling. The complex, highly sophisticated duplicating and printing systems operating at very high speeds have placed stringent requirements including narrow operating limits on photoreceptors. For example, the numerous layers used in many modern photoconductive imaging members should be highly flexible, adhere well to adjacent layers, and exhibit predictable electrical characteristics within narrow operating limits to provide excellent toner images over many thousands of cycles. Typically, negatively charged multilayered flexible photoreceptor that has been employed as a belt in electrophotographic imaging systems comprises a flexible substrate, a conductive layer, an optional blocking layer, an optional adhesive layer, a charge generating layer, a charge transport layer and a conductive ground strip layer adjacent to one edge of the imaging layers. In such a photoreceptor, it does usually further comprise an anticurl back coating layer on the side of the substrate opposite the side carrying the conductive layer, support layer, blocking layer, adhesive layer, charge generating layer, charge transport layer, and other layers to effect for curl control.
Since the charge transport layer in a negatively charged imaging member is the top outermost exposed layer, it is constantly subjected to chemical vapor contaminants exposure/interaction during electrophotographic imaging process in the field to negatively impact function. For example, exposure to the vapor amine species (from ammonia) emitted from common house cleaning agents have been seen to interact with the imaging member charge transport layer, causing material degradation to promote pre-mature onset of charge transport layer cracking and exacerbation of wear failure which severely cut short the functional life of the imaging member. In one particular instant, amine vapor impact on copy printout quality degradation has recently been seen when pre-printed papers (papers having pre-printed images which employed amine agents catalyzed UV cured ink) are used by customers for subsequent addition of xerographic images over the pre-printed paper blank spaces; that is the accumulation of amine residues deposition onto the imaging member charge transport layer surface, after repeatedly making contact with receiving papers during xerographic imaging process, is found to cause ghosting image defects print-out in the output copies. Since ghosting image defects in the output copies are unacceptable print quality failures, so it does require frequent costly imaging member replacement in the field. With all these issues and failures described above, therefore there is an urgent need to resolve these issues and extend the service life of the imaging member in the field. In particular, by the formulation of a charge transport layer that is resistive to amine specific effect to resolve the current pre-printed paper ghosting image defects print out problem.
Conventional photoreceptors are disclosed in the following patents, a number of which describe the presence of light scattering particles in the undercoat layers: U.S. Pat. Nos. 5,660,961; 5,215,839; and 5,958,638. The term “photoreceptor” or “photoconductor” is generally used interchangeably with the terms “imaging member.” The term “electrostatographic” includes “electrophotographic” and “xerographic.” The terms “charge transport molecule” are generally used interchangeably with the terms “hole transport molecule.”
In U.S. Pat. No. 7,413,835, there is disclosed an electrophotographic imaging member having a thermoplastic charge transport layer, a polycarbonate polymer binder, a particulate dispersion, and a high boiler compatible liquid. The disclosed charge transport layer exhibits enhanced wear resistance, excellent photoelectrical properties, and good print quality.
In U.S. Pat. No. 7,592,111, there is disclosed an imaging member formulated with a liquid carbonate. The imaging electrostatographic member exhibits improved service life.